GaN HEMT Back Barrier for High Breakdown Voltage
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Solution Overview
Problem
GaN-based high electron mobility transistors (HEMTs) and MOS devices face limitations in achieving high breakdown voltage and integrating p-MOS and n-MOS transistors for complementary MOS devices due to low breakdown voltage and high sheet resistance, as well as challenges in fabricating both n-type and p-type devices on the same substrate.
Innovation Solution
A high breakdown voltage structure is achieved by replacing a majority of GaN in the thick buffer stack with a back barrier comprising dilute AlGaN, which increases the band gap and resistivity, allowing for the production of both n- and p-type devices on the same substrate, enabling GaN C-MOS devices with a relaxed buffer stack and polarization stack configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick GaN buffer stack is used, then device performance is improved, but breakdown voltage remains low and sheet resistance is high
Solution Approach 1:
The patent changes the material composition parameter by introducing dilute AlGaN (2-10% Al) into the GaN buffer stack, transforming it from a pure GaN structure to a composite structure with varying aluminum content. This parameter change increases the band gap and resistivity of specific regions while maintaining the overall buffer thickness, thereby achieving high breakdown voltage without compromising sheet resistance
Solution Approach 2:
The patent creates a composite buffer stack structure combining GaN and dilute AlGaN layers. The composite structure leverages the high electron mobility of GaN while utilizing the high resistivity and band gap of AlGaN to block carrier leakage, thus simultaneously achieving low sheet resistance and high breakdown voltage through material composition optimization
2Ease of manufacture
If standard GaN buffer structure is used, then fabrication process is simple, but integration of p-MOS and n-MOS transistors is challenging
Solution Approach 1:
The patent applies local quality by creating regions with different aluminum concentrations within the buffer stack. The dilute AlGaN regions (2-10% Al) are strategically positioned to provide high resistivity for carrier blocking, while GaN-rich regions maintain high electron mobility. This spatial variation in material composition enables selective formation of both n-type and p-type devices in different device regions on the same substrate
3Reliability
If high Al content AlGaN is used to increase breakdown voltage, then resistivity increases, but electron mobility decreases
Solution Approach 1:
The patent optimizes the aluminum content parameter to a specific range of 2-10%, which is sufficiently high to provide increased band gap and resistivity for carrier blocking, yet low enough to maintain high electron mobility. This precise parameter control resolves the contradiction between breakdown voltage and electron mobility by finding the optimal aluminum concentration sweet spot
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the breakdown voltage and enables the fabrication of both n-type and p-type devices on the same substrate, improving the performance of GaN-based HEMT and MOS devices for high-performance RF switch applications and power devices, facilitating the integration of GaN C-MOS devices.
Implementation Method 1
replacing a majority of GaN in the thick buffer stack with a back barrier comprising dilute AlGaN, which increases the band gap and resistivity
Data Source
AI summary
An integrated circuit structure comprises a relaxed buffer stack that includes a channel region, wherein the relaxed buffer stack and the channel region include a group III-N semiconductor material, wherein the relaxed buffer stack comprises a plurality of AlGaN material layers and a buffer stack is located over over the plurality of AlGaN material layers, wherein the buffer stack comprises the group III-N semiconductor material and has a thickness of less than approximately 25 nm. A back barrier is in the relaxed buffer stack between the plurality of AlGaN material layers and the buffer stack, wherein the back barrier comprises an AlGaN material of approximately 2-10% Al. A polarization stack over the relaxed buffer stack.